Antimicrobial Activity and Physical Properties of Biopolymer Films Containing Supernatants of Lactobacillus sakei Growth

Introduction: Consumers’ demand for a reduction in food additives, mainly chemical preservatives, has promoted the search for several alternatives. Free cells’ supernatants of Lactobacillus growth can be incorporated as natural antimicrobials in biopolymer films, mainly to control pathogen growth in foods.

Purpose: The purpose of this study was to evaluate the antimicrobial activity and physical properties of biopolymer films containing free cells’ supernatants of Lactobacillus sakei growth. 

Methods: Calcium caseinate CAS (3% p/v) was mixed with glycerol (2%) and free-cells’ supernatants were produced by the growth of L. sakei NRRL B-1917 in MRS broth for 18h at 37°C. Films were obtained by casting. To determine films’ antimicrobial activity, circular portions of the films (0.6 mm diameter) were placed on trypticase soy agar inoculated with 10⁷ CFU/ml of S. Typhimurium, L. monocytogenes, E. coli, or S. aureus; plates were incubated (37°C) for 24h and then the inhibition halos were determined. Film thickness was measured with a micrometer; moisture was determined by weight loss, and water vapor permeability of films was measured following ASTM methodologies.

Results: The use of free cells’ supernatants of L. sakei in biopolymer films displayed inhibition halos against E. coli (4.83 ± 0.01 mm), L. monocytogenes (4.61 ± 0.02 mm), S. Typhimurium (4.21 ± 0.02 mm), or S. aureus (4.84 ± 0.02 mm). Supernatant incorporation altered films’ physical properties, increasing their thickness (0.255 ± 0.001 mm), decreasing moisture (14.27 ± 0.21%) and increasing water vapor permeability (2.01 ± 0.11 g mm/m²d kPa) in comparison to control films.

Significance: Results suggest that use of free cells’ supernatants of L. sakei growth, as natural antimicrobials could be an alternative to replace synthetic antimicrobials, due to observed antimicrobial activity against studied food pathogens.